FIG. 4 illustrates, as an example, one known prior art structure for mounting limit switches adapted to be operated with projection or retraction of an actuating rod of a linear actuator wherein the actuating rod is provided for projection and retraction with respect to an outer cylinder. In the structure shown in FIG. 4, a striker guide rod 24 and a limit switch mounting rod 25 are supported parallel to an outer cylinder 22 and between a body bracket 21 of a linear actuator 20 and a bracket 23 fixed to the front end of the outer cylinder, sleeves 26A and 27A for mounting limit switches 26 and 27 are fixed onto the limit switch mounting rod 25 so that their positions can be adjusted, and a striker 28 for actuating the limit switches 26 and 27 is slidably mounted on the striker guide rod 24.
A connecting member 30 is provided on the front end of an actuating rod 29, and one end of a striker connecting rod 31 is supported by the connecting member 30. The striker 28 is fixed to the opposite end of the striker connecting rod 31. With projecting and retracting motions of the actuating rod 29, the striker 28 slides on the striker guide rod 24, and at a retraction limit position and a projection limit position of the actuating rod 29, the striker 28 actuates the limit switches 26 and 27.
FIG. 5 shows another example of a conventional limit switch mounting structure for a linear actuator. As shown in this figure, a connecting member 42 is secured to an actuating rod 41 of a linear actuator 40, and one end of a striker supporting rod 45 is fixed to the connecting member 42. The striker supporting rod 45 supports strikers 43 and 44 at positions near both ends. The middle portion of the striker supporting rod 45 is supported for axial sliding movement by means of a guide 48 which is formed on a limit switch mounting member 47 attached to an outer cylinder 46. With a projecting or retracting motion of the actuating rod 41, the striker supporting rod 45 moves while being guided by the guide 48, and as shown in FIG. 6, the strikers 43 and 44 actuate limit switches 49 and 50, respectively, which are mounted on both sides of the limit switch mounting member 47 where the striker supporting rod 45 passes.
In the limit switch mounting structure shown in FIG. 4, it is necessary to use a striker guide rod for slidably guiding or supporting a striker or strikers, brackets for supporting the striker guide rod, and a limit switch supporting rod for mounting thereon of limit switches. Consequently, there arises the problem that the number of components required becomes larger, thus leading to an increase of production cost.
Moreover, since the limit switches are fixed onto the limit switch mounting rod through mounting sleeves, it is impossible to make the limit switch mounting spacing shorter than the mounting sleeve length. Besides, since the limit switch mounting rod and the striker guide rod are supported between the body bracket of the linear actuator and the bracket fixed on the front end side of the outer cylinder, it is impossible to mount the limit switches so as to face in a desired direction on the circumference of the outer cylinder.
Further, in the limit switch mounting structure shown in FIGS. 5 and 6, since limit switches are attached side by side to guide means, the number of limit switches capable of being mounted is limited to only two. Therefore, it is impossible to perform switching operations at three or more points within the stroke range of the actuating rod. Further, at a retracted position of the actuating rod within the outer cylinder, the striker supporting rod has a large overhang on one side of the support member, so that when the actuating rod moves at high speed, the striker supporting rod oscillates and may cause malfunction of the limit switches.